CO2 to Gasoline: The USDOE Reimagines Liquid Fuels

As we've documented many, many times now, Carbon Dioxide, as harvested from whatever convenient source, can be chemically recycled.

Carbon Dioxide can be used and consumed as the key and basic carbon-containing raw material in processes - - some of which can be powered by one form and another of freely-available, although low-grade and otherwise non-commercial, so-called "renewable" energy - - that result in the synthesis of hydrocarbon chemicals and fuels.

And, various forms of renewable energy can power those CO2 utilization processes, including sunlight, low voltage electricity generated from sunlight or wind, or, as seen for one example in our report of:

USDOE Recycles CO2 to Methanol with Solar Power | Research & Development | News; concerning: "United States Patent 6,066,187 - Solar Reduction of CO2; 2000; Inventors: Reed Jensen, John Lyman, Joe King, and Robert Guettler; Government Interests: This invention was made with government support ... (from) the U.S. Department of Energy to The Regents of the University of California. The government has certain rights in the invention. Abstract: The red shift of the absorption spectrum of CO2 with increasing temperature permits the use of sunlight to photolyze CO2 to CO. The process of the present invention includes: preheating CO2 to near 1800 K; exposing the preheated CO2 to sunlight, whereby CO, O2 and O are produced; and cooling the hot product mix by rapid admixture with room temperature CO2. The excess thermal energy may be used to produce electricity and to heat additional CO2 for subsequent process steps. The product CO may be used to generate H2 by the shift reaction or to synthesize methanol";

thermal, i,e., heat, energy, perhaps generated by concentrated solar radiation; which, in the case of the above "United States Patent 6,066,187 - Solar Reduction of CO2", is used to help power, or facilitate, the photolytic breakdown of Carbon Dioxide into Carbon Monoxide and Oxygen.

In like fashion, as in our report of:

California Thermochemical Hydrogen Production | Research & Development | News; concerning: "United States Patent 7,960,063 - Hydrogen Production by a Thermochemical Water Splitting Cycle; 2011; Inventors: Vasilios Manousiouthakis and Ioannis Manousiouthakis, Los Angeles, CA; Assignee: The Regents of the University of California; Abstract: A novel thermochemical cycle for the decomposition of water is presented. Along with water, hydrogen, and oxygen, the cycle involves an alkali or alkali earth metal based process intermediate and a variety of reaction intermediates. The cycle is driven by renewable energy sources, and can have a maximum operating temperature below 1173 K (900 C). The kinetics of the cycle are based on the reactant behavior as well as the separability characteristics of the chemicals involved";

solar-derived heat energy can be used to power what is in places called the "water-splitting" reaction, or process, with the result being the production of elemental, molecular Hydrogen and Oxygen.

And, as introduced in our report of:

USDOE Solar Thermochemical CO2-to-Fuel | Research & Development | News; concerning: "Solar Fuel Production Through The Thermochemical Decomposition of Carbon Dioxide; Nathan P. Siegel, et. al., Sandia National Laboratories, Albuquerque, NM USA; Abstract: Solar energy systems based on an intermittent resource benefit from an energy storage mechanism that decouples the solar resource from the load, enabling operation when the resource is unavailable. For utility scale power plants this is achieved with thermal energy storage (TES) systems incorporating significant volumes (some larger than 106 liters) of inorganic salts. Storing solar energy in the form of chemical fuels offers another more energy dense storage mechanism that enables the utilization of solar energy to address the energy needs of the transportation sector. Concentrating solar power (CSP) systems are capable of operating at the elevated temperatures needed to drive thermochemical reactions that convert the stable combustion products, carbon dioxide and water, first into synthesis gas, a mixture of carbon monoxide and hydrogen, and then into liquid hydrocarbon fuels such as methanol, gasoline, and jet fuel.Sandia National Laboratories (SNL) is developing a process called Sunshine to Petrol, or S2P, in which a two-step thermochemical cycle is used to produce synthesis gas via H2O and/or CO2 decomposition that may then be converted into a liquid hydrocarbon fuel";

the United States Government, via the USDOE's Sandia National Laboratories headquartered in New Mexico, has established a formal development program, "Sunshine to Petrol, or S2P', directed to establishing the technology for using solar-derived thermal energy to break CO2 and H2O down together into Oxygen, and into "a mixture of carbon monoxide and hydrogen", which, together, comprise hydrocarbon "synthesis gas" which, through known and established processes, can then be catalytically, chemically condensed into such seemingly-desirable stuff as "methanol, gasoline and jet fuel".

And, herein, we see that our US Government, in respect of the apparent success of the "S2P", solar-driven CO2-to-fuels program, is actually urging us to "Reimagine" how we might in the future supply our economy with liquid hydrocarbon fuels, via the recycling, the productive and profitable use, of Carbon Dioxide.

(We don't wish to clutter our presentation herein overmuch, so we won't cite specifics. But, a number of the above-named USDOE scientists have figured in quite a few of our prior reports about USDOE-sponsored Carbon Dioxide utilization developments.)

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Abstract: The vision of Sunshine to Petrol is captured in one deceptively simple chemical equation:

Solar Energy + xCO2 + (x+1) H2O → CxH2x+2(liquid fuel) + (1.5x+.5) O2

Practical implementation of this equation may seem far‐fetched, since it effectively describes the use of solar energy to reverse combustion. However, it is also representative of the photosynthetic processes responsible for much of life on earth and, as such, summarizes the biomass approach to fuels production.

It is our contention that an alternative approach, one that is not limited by efficiency of photosynthesis and more directly leads to a liquid fuel, is desirable. The development of a process that efficiently, cost effectively, and sustainably reenergizes thermodynamically spent feedstocks to create reactive fuel intermediates would be an unparalleled achievement ... .

We proposed that the direct thermochemical conversion of CO2 and H2O to CO and H2, which are the universal building blocks for synthetic fuels, serve as the basis for this revolutionary process. To realize this concept, we addressed complex chemical, materials science, and engineering problems associated with thermochemical heat engines and the crucial metal‐oxide working‐materials deployed therein.

By project’s end, we had demonstrated solar‐driven conversion of CO2 to CO, a key energetic synthetic fuel intermediate, at 1.7% efficiency.

(The above "1.7% efficiency" might not sound all that encouraging. It is, however, more than good enough. It compares well with the efficiency of natural photosynthesis, and doesn't sacrifice arable farm land in service to exploitive and wasteful food-for-fuel sacrifices like Corn Ethanol. And, the Earth gets more than enough solar thermal energy to make up for the seeming inefficiency.)

Practical implementation of this equation seems far‐fetched because it effectively describes using solar energy to reverse combustion. However, it also describes photosynthesis and, as such, summarizes the biomass approach to producing fuel.

(But without the sacrifice of cropland.)

Regrettably, photosynthesis and consequently the biofuels approach have a very low sunlight‐to‐hydrocarbon conversion efficiency and suffer from a number of other shortcomings.

Thus, developing an alternative approach that more‐directly and efficiently produces a liquid fuel is desirable. Developing a process that sustainably and cost effectively reenergizes thermodynamically spent feedstocks to create reactive fuel intermediates would be an unparalleled achievement ... . Our proposition was that the direct thermochemical conversion of CO2 and H2O to CO and H2, which are the universal building blocks for synthetic fuels, should serve as the basis for this revolutionary process. To realize this concept, we addressed complex chemical, materials science, and engineering problems associated with thermochemical heat engines and the crucial metal‐oxide working materials deployed therein.

Energy resources are the foundation for developed economies and are inextricably linked to national security, social stability, and quality of life. The nation’s increasing reliance on costly imported petroleum and fuels and “peak oil” concerns create an increasing vulnerability to potentially high‐consequence supply disruptions.

Diversification of supplies, including developing additional independent, domestic sources of transportation fuel, is essential for the future security and economic well‐being of the US.

Independence from energy imports can be achieved to a great degree through the utilization of less‐conventional hydrocarbon resources such as coal ... , (but we) must recognize that hydrocarbon fuels are energy carriers, not energy sources. That is, with an appropriate persistent energy source, there is the potential to effectively reverse combustion and “reenergize” CO2 and H2O back into hydrocarbon form in a process analogous to, but more direct and efficient than, the one that produced fossil fuels.

We call this process “Sunshine to Petrol” or S2P.

Solar insolation is a very attractive persistent energy source as it is by far the largest exploitable renewable resource and is technically capable of supplying all of the global energy needs utilizing only a few per cent of the world’s desert area. However, the efficient conversion of solar energy to stored chemical energy in the form of hydrocarbons is a significant challenge. Photosynthesis is the biological route for accomplishing this conversion, but the sunlight‐to‐stored chemical energy efficiency is limited by the photosynthetic step alone to only a few percent on average. The most general and straightforward chemical approach to converting CO2 and H2O into a fuel is through the intermediate production of syngas. Syngas is roughly a 1:2 mixture of CO and H2. That is, the key to chemically converting CO2 and H2O into fuel is the following “reenergizing” reaction: 2CO2 + 4H2O → 2CO + 4H2 + 3O2.

Of course, the reduction of CO2 and H2O (carbon dioxide splitting, CDS, and water splitting, WS) may be carried out individually rather than in a single step or apparatus. Once syngas is obtained, there are numerous commercial processes for the subsequent production of liquid fuels, including alcohols, ethers (e.g., methanol and dimethyl ether), gasoline, jet fuel, diesel and other products.

The reactions leading to hydrocarbons from syngas are thermodynamically “downhill” at the applicable temperatures. Thus, the most challenging and energy‐consuming chemical processes required for closed cycle hydrocarbon manufacture and use is syngas production, i.e. CDS and WS. Hydrogen can of course be produced electrolytically from water. Selective electrochemical reduction of CO2 is not yet a realistic alternative, but CO can be produced from H2 and CO2 with additional energy input via the endothermic Reverse Water Gas Shift (RWGS) reaction: CO2 + H2 = CO + H2O.

(Again, we're not including many separate reference links, since this USDOE exposition can stand fully on it's own. But, we have separately documented all of the above in past reports archived by the West Virginia Coal Association.)

A reasonable annual average estimate for the photovoltaic‐powered water electrolysis step is 7% efficiency. In this case, the primary factor limiting solar‐to‐chemical efficiency is the conversion of sunlight to electricity, as electrolytic system efficiencies of 73% have been reported. Avoiding the solar to electric conversion altogether is a potentially attractive avenue for further improving the efficiency. However, thermolysis of water is not thermodynamically favorable even at the impractically high temperature of 3000 C. Furthermore, if direct dissociation were to be accomplished, it would remain to perform a difficult high temperature quench and H2/O2 separation. The elegant work‐around for these problems is to couple two or more chemical reactions that sum to WS, and then perform these reactions in a cyclic manner, recycling all the reactants and products other than H2O, H2, and O2. Conceptually, thermochemical cycles are heat engines that drive endothermic chemical reactions and that have the potential to be more efficient than electrolytic approaches. The basic thermodynamic principles are described elsewhere.

Concentrating solar power (CSP) provides efficient utilization of solar energy and access to temperatures in excess of 1500 °C. This allows the consideration of CSP‐driven ultra‐high temperature two‐step metal oxide based cycles. An example of a thermochemical WS cycle based on a hypothetical metal oxide working material (MOx) is shown below. CDS is entirely analogous. Thermodynamics requires that the two chemical reactions of the cycle be carried out at different temperatures: the endothermic thermal reduction of the metal oxide (TR) at a high temperature, and the exothermic H2‐producing oxidation step (WO) at a lower temperature. It is necessary therefore to cycle the temperature of the oxide as well as the gaseous environment.

Briefly, at the highest level the goal of this project was to establish credibility for the S2P approach to fuels from sunlight. This was understood to mean that the effort needed to demonstrate that the approach is technically sound, that there is a realistic pathway to economic and commercial viability, and that the approach is scalable to the extent that it could potentially meet a large fraction of U.S. liquid fuel demand. Specific high level goals derived from this vision included demonstrating the thermochemical conversion of CO2 to CO at a solar-to-fuel efficiency of 2%, demonstrating a pathway for 5% efficiency, and defining an approach to 20%.

In other words, it was understood from the beginning that the three‐year time frame of the project would be insufficient to produce a commercial product given the immaturity of the associated science and technology. However, the time frame would allow for the development of the underlying science and tools needed to provide a very strong basis to move the field of thermochemistry forward. Keeping an eye towards larger systems and economics issues was deemed vital as well so that the work would be relevant and so that a community of interest and support could be built with confidence".

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Much of the remainder of the report is like-worded somewhat inconclusive rhetoric, encouraging in as unassertive way as seemingly possible the continuation of efforts to improve and reduce to practice a system which can use solar heat energy, facilitated by metal oxide catalysts, to convert Carbon Dioxide and water into Carbon Monoxide and Hydrogen, which can then be catalytically, chemically condensed into hydrocarbon fuels like "methanol and dimethyl ether, gasoline, jet fuel, diesel", etc.

Mention is made of the Counter Rotating Ring Receiver Recuperator, "CR5" developed at the Sandia Lab and we featured in a number of our earlier reports. Those reports were made so long ago now, though, that we've found it impossible to winnow them out of the thousands stored in the West Virginia Coal Association's R&D archive files. The device, though, is explained and described in a now nearly-ancient news release from the Sanida National Lab:

https://share.sandia.gov/news/resources/releases/2007/sunshine.html; "December 5, 2007; Sandia’s Sunshine to Petrol project seeks fuel from thin air; Team to chemically transform carbon dioxide into carbon-neutral liquid fuels; ALBUQUERQUE, N.M. - - Using concentrated solar energy to reverse combustion, a research team from Sandia National Laboratories is building a prototype device intended to chemically “reenergize” carbon dioxide into carbon monoxide using concentrated solar power. The carbon monoxide could then be used to make hydrogen or serve as a building block to synthesize a liquid combustible fuel, such as methanol or even gasoline, diesel and jet fuel. The prototype device, called the Counter Rotating Ring Receiver Reactor Recuperator (CR5, for short), will break a carbon-oxygen bond in the carbon dioxide to form carbon monoxide and oxygen in two distinct steps. It is a major piece of an approach to converting carbon dioxide into fuel from sunlight.The Sandia research team calls this approach “Sunshine to Petrol” (S2P). “Liquid Solar Fuel” is the end product - - the methanol, gasoline, or other liquid fuel made from water and the carbon monoxide produced using solar energy".

USDOE Solar CO2 Recycling Supplemental Technology | Research & Development | News; concerning, in part: "United States Patent 7,140,181 - Reactor for Solar Processing of ... Transparent Gases; 2006; Inventors: Reed Jensen, NM, et. al.; Abstract: Solar-powered reactor for processing of slightly absorbing and transparent gases. An obvious path to providing storable, renewable energy is through solar dissociation of gas molecules. These dissociation products are the precursors of modern liquid and gaseous fuels such as hydrogen and methanol/ethanol. An apparatus and method using a solar concentrator (such as a focusing trough or dish) directed at the receiving end of a reactor are disclosed. A range of designs of reactors for the dissociation of gases, both those that absorb slightly in the visible spectrum and those that are transparent in the visible and only absorb in the infrared, is described. For slightly-absorbing gases, a funnel-shaped reactor that preheats the gas and concentrates sunlight is the indicated embodiment. A system for dissociating CO2 using the invention is described (and) heat from the hot stream of dissociated gas may also be used to produce electricity… Claims: A method for solar powered processing of a slightly-absorbing or transparent gas, comprising the steps of: passing the process gas through a reaction zone; concentrating incoming solar radiation in the reaction zone to drive an endothermic dissociation reaction in the process gas ... . (And) wherein the process gas is CO2. A primary object of the present invention is to provide an apparatus for ... the process of solar disassociation of molecules into fuel precursors. .... (A) solar powered endothermic reactor apparatus for processing slightly-absorbing or transparent gases ... (which) ... results in ... photolysis and pyrolysis of CO2 to CO by concentrated solar light".

Clearly, or at least so it would seem, this is not technology that would lend itself well to implementation in West Virginia, Pennsylvania, Kentucky and most other parts of often-cloudy US Coal Country. But, wouldn't we all much rather be buying "gasoline, diesel and jet fuel" made out of Carbon Dioxide in, say, Florida, than continue to purchase such vital commodities, as made from natural petroleum, from the friendly proprietors of OPEC? And, wouldn't we welcome the relief from threatened Carbon taxation of our economically essential Coal-fired generators of abundant and currently-affordable electricity in Coal Country?

Also clearly: The United States Government has used the taxes paid by all of us to develop technology that would allow us to start treating the Carbon Dioxide co-produced by our use of Coal in the generation of that reliable and economically essential electricity as a valuable raw material resource.

And, it seems far past time the tax-paying US citizens of US Coal Country, whose livelihoods and cherished ways of life are threatened by assaults against the Coal-fired power generation industry based on concerns over Carbon Dioxide emissions, were told all about it.

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